The disclosures of Japanese Patent Application Nos. 2001-100769 and 2001-102301 both filed on Mar. 30, 2001 each including the specification, drawings and abstract, are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a dynamic damper for use in a steering system of an automotive vehicle, which is adapted to be fixed to a steering column or a steering wheel for the purpose of absorbing vibrations excited in the steering wheel.
2. Description of the Related Art
A steering wheel of an automotive vehicle is a member for allowing an operator of the vehicle to steer the vehicle. The operator of the vehicle almost always handles directly the steering wheel during driving the vehicle, and eventually is able to sensitively feel minute vibrations excited in the steering wheel. Since the vibrations excited in the steering wheel greatly impact on a riding comfort of the vehicle as felt by the operator, there has been a great regard for absorbing the vibrations excited in the steering wheel.
In an attempt to damp or attenuate vibrations excited in the steering wheel, a dynamic damper has been mounted on the steering wheel or other members of the steering system, thereby providing a secondary vibration system for the steering system as a primary vibration system. A natural frequency of the secondary vibration system is tuned to a natural frequency of the steering system, so that the vibrations excited in the steering wheel may be damped.
An extensive study of the dynamic damper for use in the steering system conducted by the present inventors has revealed the fact that the adoption of the conventional dynamic damper does not always effectively prevent the vibrations of the steering wheel, especially in recent automotive vehicles.
It is therefore one object of this invention to provide a dynamic damper for use in a steering system, which is novel in construction and which is capable of exhibiting an excellent vibration damping effect with respect to vibrations excited in a steering wheel of the steering system in an effective and stable manner.
In order to achieve this object of the invention, the present inventors has conducted eager studies of steering systems adopted in recent automotive vehicles, and has revealed that a natural frequency of the steering system has been shifted to a high frequency band as a result of a recent tendency for steeling wheels to be made of light metals including aluminum alloy and a magnesium alloy rather than conventionally employed ferrous metals, for the purpose of improving a steeling feeling.
Further intensive studies of the steering systems carried by the present inventors has also revealed that a frequency band of idling vibrations acting on the steering wheel has been shifted to a low frequency band as a result of a recent tendency for decreasing an engine speed of an internal combustion engine during its idling state for the purpose of improving fuel economy.
Also, the present inventors has studied about automotive vehicles equipped with the conventional steeling wheel whose reinforcing member is made of ferrous metal, and has revealed that the steeling system equipped with the conventional steeling wheel generally has a natural frequency at around 20-30 Hz, which is approximately identical with the frequency band of the idling vibration excited in the general conventional automotive vehicle.
With the above-described revealed facts taken into synthetic consideration, it may be concluded that the vibrations, e.g., the idling vibration, excited in the steering wheel of the conventional steering system has been effectively damped by attaching a single dynamic damper to the steering wheel or the steering column of the steeling system, and by tuning a natural frequency of the single dynamic damper to the natural frequency band of the steeling system. However, the recent development in the automobile technology provides not only the above-indicated structural change in the steeling system but the above-indicated change in the internal combustion engine as well. Eventually, the conventional dynamic damper becomes incapable of exhibiting a desired vibration damping effect with respect to the vibrations excited in the steeling wheel. In particular, the conventional dynamic damper is tuned on the basis of the natural frequency of the steeling system, so that the use of the conventional dynamic damper in the recent automotive vehicles may cause undesirable deterioration of vibration conditions of the steeling wheel at a lower and higher frequency bands adjacent to the tuning frequency of the dynamic damper (i.e., the natural frequency of the steering system). In addition, since the frequency band of the idling vibrations is made lower than the natural frequency of the steering system in the recent vehicle, the conventional dynamic damper attached to the steeling system of the recent vehicle may conversely deteriorate the vibration conditions of the steeling wheel in comparison with the case where no dynamic damper is attached to the steeling system. For the above reasons, the present inventors could theorize the tendency of deterioration of the vibration condition in the steering system of the recent vibrations.
In addition, the present inventors has studied about a tilting type steering system that has been widely adopted in the recent automotive vehicles, and revealed that the natural frequency of the tilting type steering system sometimes changes when the position of the steering wheel is changed by means of a steering-wheel position mechanism of the tilting type steering system. That is, the natural frequency of the tilting type steering system may deviate from the tuning frequency of the dynamic damper depending upon the position of the steering wheel, inevitably deteriorating the vibration condition of the steering wheel.
The present invention has been developed on the basis of the above-described knowledge acquired by the present inventor through their eager studies of the steering system, and provides a dynamic damper to cope with the problem of vibrations in the recent steering wheel.
The above and/or other objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principal of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A dynamic damper for use in a steering system of an automotive vehicle, comprising: (a) a mounting member adapted to be fixed to a steering column or a steering wheel of the steering system; and (b) a plurality of secondary vibration systems each including a mass member and a spring member for elastically supporting the mass member with respect to the mounting member, the plurality of secondary vibration systems being independent of each other, wherein at least one of the plurality of secondary vibration systems has a natural frequency that is tuned to an idling vibration frequency band ranging from about 20 Hz to about 30 Hz, and at least an other one of the plurality of secondary vibration systems has a natural frequency that is tuned to a natural frequency band of the steering system, which is larger than 30 Hz.
As discussed above, the present inventors has studied in detail about vibrations excited in the steering system, which has not sufficiently been regarded or clarified conventionally, and theoretically and experimentally recognizes that the use of a plurality of dynamic dampers one of which is tuned to the natural frequency of the steering system, and another of which is tuned to the idling vibration frequency band, is effective in order to damp vibrations excited in the steering wheel. In view of the above, the dynamic damper of the present invention includes a plurality, e.g., two of the secondary vibration systems, which are substantially independent of each other and tuned to the natural frequency of the steering system and the idling vibration frequency band, respectively. Thus, the present dynamic damper is capable of stably exhibiting a high damping effect with respect to the vibrations excited in the steeling wheel, if the dynamic damper is mounted on the steering system of the recent vehicle.
(2) A dynamic damper according to the above indicated mode (1), wherein the steering wheel of the steering system includes a reinforcing member made of light metal including an aluminum alloy and an magnesium alloy. In this mode of the invention, one of the plurality of the second vibration systems is tuned to the natural frequency of the steering system, although the natural frequency of the steering system is made higher than the idling vibration frequency due to the use of the reinforcing member made of the light metal. Thus, the dynamic damper of this mode of the invention is capable of preventing resonance of the steering wheel upon application of a vibrational load whose frequency is higher than the idling vibration frequency.
(3) A dynamic damper according to the above-indicated modes (1) or (2), wherein the spring member of each of the secondary vibration systems whose natural frequencies are tuned to the idling vibration frequency band and the natural frequency band of the steering system, comprises an elastic support member adapted to undergo shear deformation in a direction perpendicular to a central axis of the steering column. In this mode of the invention, the spring member is able to exhibit a relatively low spring constant, in comparison with the case where the spring member is adapted to undergo compression deformation, making it possible to tune the natural frequency of each of the secondary vibration systems to the natural frequency of the steering system or the idling vibration frequency band, while avoiding or minimizing an enlargement of the mass member and deterioration of the durability of the spring member.
(4) A dynamic damper according to the above indicated mode (3), wherein the elastic support member of each of the secondary vibration systems whose natural frequencies are tuned to the idling vibration frequency band and the natural frequency of the steering system, has a circular shape in cross section extending in the direction perpendicular to the central axis of the steering column. In this mode of the invention, the dynamic damper is able to eliminate or minimize the possibility of undesirable changes in the natural frequency of each secondary vibration system, if a vibration input direction with respect to the spring member changes due to the turning of the steering wheel, for example. Thus, the dynamic damper of this mode of the invention is capable of exhibiting an excellent vibration damping effect with high stability, with respect to vibrations applied thereto in different radial directions.
(5) A dynamic damper according to the above-indicated mode (3) or (4), wherein at least one of said each of said secondary vibration system is arranged such that the elastic support member has a principal elastic axis that is approximately in conformity with a principal inertia axis of the mass member in a direction in which the mass and the mounting member are opposed to each other. In this mode of the invention, the dynamic damper is able to stabilize vibration attitude or condition of the mass member upon application of the vibrational load in radial directions perpendicular to the central axis of the steering column, making it possible for the dynamic damper to exhibit a desired vibration damping effect in a more effective and stabile manner.
In this mode (5) of the invention, the principal elastic axis of the elastic support member may preferably be located close to a center of gravity of the mass member, for thereby further stabilizing vibration attitude of the mass member. Namely, this arrangement is effective to prevent or minimize a rotative or a tilting motion of the mass member when the dynamic damper is subjected to the vibration in the direction perpendicular to its central axis, permitting the dynamic damper to exhibit a desired vibration damping effect in a further effective and stable manner. In order to locate the principal elastic axis of the elastic support member close to the center of gravity of the mass member, the dynamic damper may have a variety of configuration. For instance, the mass member may have a cylindrical shape and is disposed radially outwardly of the elastic support member so as to protrude toward the side of the bracket, so that the principal elastic axis of the elastic support member is located close to the center of gravity of the mass member effectively.
(6) A dynamic damper according to any one of the above-indicated modes (1)-(5), wherein the spring member of at least one of the plurality of secondary vibration systems comprises a plurality of elastic support members extending parallel to each other while having a circular cross section.
According to this mode of the invention, the spring member is composed of the plurality of elastic support members each having a circular shape in cross section, so that each elastic support member can exhibit substantially the same spring characteristics in all radial directions perpendicular to its axial direction. As a result, the dynamic damper is capable of exhibiting substantially the same damping characteristics with respect to the vibrations applied thereto in various radial directions perpendicular to the central axes of the elastic support members. While the dynamic damper for use in the steering system is likely to be subjected to vibrations whose directions vary in various radial directions perpendicular to the central axis of the steering column due to the turning of the steeling wheel, the dynamic damper of this mode of the invention is able to function as the effective secondary vibration system with respect to the vibrations applied thereto in the various radial directions.
In addition, the use of the spring member in the form of the plurality of elastic support members makes it possible to dispose the elastic support members on respective portions remote from the center of gravity of the mass member, for elastically supporting the mass member by the spring member. Namely, this arrangement makes it possible to position actual support points of the elastic support members for supporting the mass member on the portions remote from the center of gravity of the mass member, thus assuring an excellent stiffness of the spring member (i.e., the plurality of the elastic support members) in its entirety for supporting the mass member upon rotation of the mass member. Therefore, the dynamic damper of this mode is able to exhibit a desired vibration damping effect with high stability.
(7) A dynamic damper according to the above-indicated mode (6), wherein the plurality of elastic support members are located close to an outer peripheral portion of the mass member rather than a center of gravity of the mass member, in a plane perpendicular to central axes of the plurality of elastic support members. In this mode of the invention, the elastic support members cooperate to elastically support the mass member with further improved stability, while preventing irregular deformation of the mass member. Thus, the dynamic damper of this mode is able to exhibit a desired vibration damping effect with further improved stability.
(8) A dynamic damper according to the above indicated mode (6), wherein a general principal elastic center of the plurality of elastic support members extends in a direction of central axes of the plurality of elastic support members, and is approximately in conformity with a principal inertia axis of the mass member. This arrangement is effective to stabilize a vibration attitude or condition of the mass member upon application of the vibrational load in the directions perpendicular to the central axes of the elastic support members, so that the dynamic damper is able to exhibit the desired vibration damping effect with high stability. This mode of the invention may effectively embodied, such that the plurality of elastic support members are disposed on a circumference about the principal inertia axis of the mass member so as to equally spaced apart from each other in the circumferential direction, and so as to extend parallel to the principal inertial axis of the mass member, for example.
In this mode of the invention, the center of gravity of the mass member is preferably located close to the general principal elastic axis of the plurality of elastic support members, for thereby stabilizing the vibration attitude of the mass member, e.g., preventing or minimizing a rotative or a tilting motion of the mass member when the dynamic damper is subjected to the vibration in the direction perpendicular to the central axes of the elastic support members. Thus, the dynamic damper of this mode is able to exhibit a desired vibration damping effect in a further effective and stable manner. In order to locate the general principal elastic axis of the elastic support members close to the center of gravity of the mass member, the mass member may be arranged so as to protrude toward the mounting member around the elastic support members.
(9) A dynamic damper according to the above-indicated mode (6), wherein a general principal elastic center of the plurality of elastic support members extends parallel to a central axis of the steering column. In this mode of the invention, the dynamic damper is subjected to vibrations applied thereto in various radial directions perpendicular to the central axis of the elastic support members. Since each elastic support member extends parallel to the central axis of the steering column with a circular shape in cross section, the dynamic damper can exhibit the desired vibration damping effect with high stability when the direction of the applied vibration is changed upon rotation of the steering wheel.